test: reduce flakiness in pdf test

[nornagon]

Description of Change

This is a bit hacky, since really we ought to wait for the pdf frame to load, but I haven't been able to reproduce this test failing locally so I'm not sure what situation is causing it to fail.

For now, as this is one of our flakier tests, I think on balance there will be less total pain if we remove (what I assume is) the flaky bit from this test. Perhaps this is masking another bug, but I don't know what it is if so.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• PR title follows semantic commit guidelines

Release Notes

Notes: none

[samuelmaddock]

After #25385 is merged, the extension-ready event can be awaited for when the PDF extension is fully loaded. If the flakiness is caused by it not yet being loaded, this could fix it.

[nornagon]

@samuelmaddock interesting, i'm not sure that's the case though as the pdf extension is a built-in extension, so it should be ready before any web contents are created, right?

[release-clerk]

No Release Notes